Soluble alkali metal silicate glasses and most glasses are prepared by charging raw materials into a furnace heated to 1093.degree.C (2000.degree.F) or more to melt and react the raw materials and form a bed of molten silicate glass. The raw materials are usually called "batch" and in producing soluble silicate glass it consists essentially of a source of sodium such as sodium carbonate and a source of silica such as sand. The "batch" is charged to the furnace and floats on the molten glass until it melts and reacts to become part of the glass bed. The materials that form the "batch" have dissimilar densities which tend to cause segregation of the components, in batching operations and in the furnace prior to melting. The segregation in the furnace is brought about partly by bubbles of CO.sub.2 which are liberated and rise from the soda ash and rising through the unreacted and unmelted "batch". Non-uniform products and losses of raw materials can also be caused by the rush of combustion gases through oil or gas fired furnaces. These high velocity gas streams entrain particles of raw materials, usually the lighter soda ash and carry them out of the furnace or into various parts of the furnace superstructure. In the usual practice of most glass makers the molten bed is quiescent except for slow moving convection currents that are set up between areas of different bed temperatures throughout the furnace. The effect of these convection currents is rather limited. One method of alleviating these problems is to carry out the fusion at a higher temperature and for a longer period of time, increasing the effect of the convection currents thereby producing a somewhat more homogeneous product. Although this is the usual practice in the glass industry there is a considerable energy penalty associated with it.
Another difficulty encountered by the soluble silicate industry is that of reducing the particle size of the product glass. In general, soluble silicate glasses are tough and resist fracturing so that grinding and other methods of sub-division must be used to produce small glass particles that dissolve more quickly. Such processes are also energy intensive and introduce impurities into the resulting ground materials and subsequently into the solutions prepared from such material.
A problem that is not of importance to the soluble silicate industry but is of prime importance to the glass industry, is the removal of seeds or gas bubbles from the glass. These gas bubbles which may be CO.sub.2 or air do not separate from the glass spontaneously, primarily because of the viscous nature of the glass. Apparently this problem which essentially is one of refining the glass, can be alleviated by bubbling steam and then oxygen through the molten glass to remove the entrapped gas bubbles as shown by Shadduck in U.S. Pat. No. 2,331,052. A similar system of refining, and in this case mixing the molten glass, is shown by Arbeit in U.S. Pat. No. 3,015,190 in which gases, including steam, are bubbled through a very limited portion of the molten glass in a conduit. In both these patents a limited number of bubblers are employed directly in a zone of molten glass influenced by a burner. Also, the bubbling provided in these systems is relatively slow and bubbles of the steam and/or oxygen do not remain in the glass after it is drawn from the furnace and cooled. A third process involving steam bubbling is described by Fenstermacker in U.S. Pat. No. 3,617,231 which relates to controlling the working temperature of glass by addition of water supplied by steam bubbling. In this process the steam bubbling is confined to a forehearth through which the glass is drawn after melting and refining.
It is an object of the invention of this application to provide a method whereby homogeneous glass can be prepared without using higher fusion temperatures for longer periods, but in fact uses lower temperatures and shorter periods, thereby saving fuel or increasing production. It is a further object of this invention to provide glass that contains bubbles and is therefore easily shattered or fractured, and dissolves up to 40% faster than glass that has not been subjected to steam bubbling.